The oldest public wildflower garden in the United States
Leafy Spurge (Wolf's Milk)
Euphorbia virgata Waldst. & Kit.
Upland - subject to control
Late Spring - Summer
Leafy Spurge is an invasive perennial plant that is considered a Noxious Weed with prohibited seed distribution. It has smooth stems that are 2 to 3-1/2 feet high, erect and branching near the top.
Leaves are alternate on the stem, linear, with leaf margins parallel or almost parallel at midleaf. The tips are pointed to obtuse. On the upper stem below the inflorescence they become more lance-like (wider at the base) and there is usually a small whorl of bracts beneath the inflorescence accompanied by a pair of opposite leaves below the whorl. Within the inflorescence there are a few bracts that are more lanceolate in shape (widest at or just below the middle). The stems, flowers and leaves will emit a white milky toxic sap if broken.
The inflorescence is a terminal umbel-like arrangement of cyathiums, up to 5 inches wide. Stemmed cyathiums also grow from the leaf axils below. The terminal cluster contains 5 to 17 branches which all form at the same time. Each of these branches can be branched once or twice again.
The flowers are very small, yellowish-green and are borne just above a showy yellow-green bract that forms early in the season on each branch of the umbel. The bract has a special name - a cyathium - within which appear unisexual flowers. Plants of the Euphorbia genus are somewhat unique in this regard. A cyathium is a cup-like structure and inside at its base are nectar glands (greenish-yellow in this species) and these have outward flaring appendages that look like petals. From this base around the nectar glands appear the male flowers, 10 to 25 in this species, which are without a perianth and have one stamen each. Rising from the center of the cyathium is the stalk of the single female flower, which is without a perianth and consists only of a bare green 3-lobed ovary with a three-branched style emerging.
Seed: Mature female flowers eventually produce 3 oval seeds, 3 to 5 mm long. Seeds disperse up to 15 feet, explosively from a seed capsule, have a high germination rate and will survive up to 7 years in the soil. While it is non-native, it is commonly found throughout Minnesota after introduction from Europe.
It is invasive and toxic. (see below).
Habitat: Leafy Spurge grows from a stout caudex which has a deep vertical root and reproduces from seeds and primarily from the underground crown and root buds, which are numerous. Tilling the soil and breaking up the root results in greater growth of the population as a single root bud will create a new plant. It is a common plant of roadsides, dry fields and hillsides and is most aggressive in dry areas. It is allelopathic, that is, it has chemicals that inhibit other forbs from growing near it.
Names: The genus name, Euphorbia, is said to refer to Euphorbus, the Greek physician of King Juba II of Numidia. Euphorbus found medicinal uses of certain plants of this genus. Carl Linnaeus named the genus after him. The species, virgata, usually means 'twiggy' and is probably a reference to the way the inflorescence appears with numerous cyathiums on long stalks sticking out in numerous directions. The Euphorbias are a large world-wide genus. There are 14 members of the genus with known populations in Minnesota (as of 2019) and several others were once reported but there are no collected specimens.
The author names for the plant classification from 1803 - 'Waldst. & Kit.' refer to Franze de Paula Adam von Waldstein (1759-1823), an Austrian explorer and naturalist. He studied the botany of Hungary with Pál Kitaibel (1757-1817), Hungarian botanist and chemist who was a professor of botany and chemistry at Pest. Together they published Descriptiones et icones plantarum rarorum Hungariae in 3 volumes in 1802-1812. Waldstein's younger brother Ferdinand Ernst Gabriel was a patron of Ludwig von Beethoven, from which acquaintance came the Waldstein Sonata.
A name sometime applied to this species is E. escula but research reported by Flora of North America, Vol. 12, states that there are only a few herbarium examples that match that species and they are localized to a time period of the late 1800s and early 1900s and do not match current populations. E. escula is restricted to certain parts of Europe and not widespread like E. virgata. The former has leaf blades that are more oblanceolate to obovate-elliptic with the margins not parallel in midleaf. All Minnesota authorities list our plant as E. virgata.
Comparisons: Another Euphorbia that is native to Minnesota, not invasive, and grown as an ornamental for its many late summer white flowers is Flowering Spurge, Euphorbia corollata. Another Euphorbia found at Eloise Butler is the Wild Poinsettia, Euphorbia cyathophora.
Above: 1st photo - Note the yellowish-green bracts which show off the small flowers. 2nd photo - Leafy Spurge growing invasively within a community of other plants.
Below: 1st photo - Flower buds developing. 2nd photo - Each branch of the inflorescence bears a cyathium - a cup-like structure. As shown here these can have a first level with a second series rising from the first - in this case two additional cyathium are rising on stalks from the first, which has in its center a set of male and female flower parts. The upper sections are developing their own reproductive parts. A third level rising from the second is possible.
Below: 1st photo - In the center of the lower cyathium are yellow-green nectar glands, each with a pair of outward flaring appendages. Beneath these are the male flowers which each put up a single stamen; and flopped over on its side is the female ovary with the three-branched style. Branching upward around them are another pair of cyathiums. 2nd photo - The fertilized ovary has swollen in size showing the characteristics 3 chambers. Below are the remains of the nectar glands and the male flowers and above is the decaying style on the ovary. To the upper right is a second cyathium with its own set of flower parts, but development looks aborted.
Below: When the seed capsule is mature it splits open explosively and dispels the seed. Each ovary can produce 3 seeds. At left are the pieces of a seed capsule, a green immature seed and an almost mature brown mottled seed.
Below: 1st photo - The narrow linear leaves of the stem below the inflorescence. 2nd photo - The characteristic whorl of leaves just below the branching of the inflorescence with a pair of opposite leaves below the whorl.
Below: When uncontrolled, Leafy Spurge will form large masses, blocking sunlight from other plants and secreting a chemical that prevents other plants from growing.
Noxious Plant Notes: Leafy Spruge is generally classified as a noxious weed and in Minnesota as invasive, thus it is regulated by being on the list of Prohibited Noxious Weeds. 22 states have the plant on some type of control list. It is found in all the lower Canadian Provinces and all the states of the lower 48 except those in the far Southeast. Within Minnesota two thirds of the counties report it. It arrived in the Wildflower Garden sometime between 1951 and 1986.
The seed capsule can emit seeds explosively up to 15 feet from the plant. The seed remain viable for up to seven years. Like most noxious weeds it is tolerant of a wide range of habitats with the main threat being to prairies and savannas where it can quickly displace native species. In 1982, then Garden Curator Ken Avery recruited volunteers to help control it in the Garden. Prescribed burning with an application of glyphosate and 2,4-D works, but not in a native plant area. The Minnesota DNR states that the most effective eradication method for a small patch is with Picloram, but only as a last resort as the chemical persists in the environment. Certain root boring beetles are known to provide biological control as explained below. It is believed the plant arrived in the U.S. in the early 19th century as a seed impurity. It was first recorded in Massachusetts in 1827.
Toxic: The milky latex juice of the plant has toxic effects on humans and animals. Foraging on the plant has been known to be deadly to animals. They can't digest it and it produces a stomach ache. Goats and sheep, however, eat it. There is some concern that the toxin is carcinogenic to humans. Kinghorn, in his book, Toxic Plants (Ref. #15), devotes an entire chapter to the carcinogenic and irritant properties of the Euphorbiaceae and details some of the chemicals found in this species.
Control experiment: In the western grasslands Leafy Spurge has infested almost 800,000 hectares in Montana, the Dakotas and Wyoming. Grazing domestic sheep helps control the plant if the sheep have access to it early in the plant's life cycle. The plants then produce fewer flowers and seeds. An study by Eva Masin, University of Montana, determined that grazing sheep preferred non-native forbs such as Leafy Spurge when they were in abundance compared to native forbs. In her study area, sheep grazed 89% of the non-native forbs vs 28% of the native forbs. This of course, may be due to the higher non-native population to begin with, but it does show that infestations on rangeland can be mitigated by grazing. (Info from Kelseya, Winter 2011, Montana Native Plant Society)
Biological control: Other control methods involve using the Flea Beetle and the Leafy Spurge Stem-boring Beetle, which lays eggs in the roots and the hatching larva eat the roots. Simply taking the time to cut down the stalks before seed production will greatly reduce numbers over time. (Info from Kelseya, Fall 2014, Montana Native Plant Society)
The University of North Dakota reports success with the flea beetle, which they first released in the early 1990s. Treated areas have seen a 50% reduction in plants. The adult beetles feed on leaves, but most help comes from the larvae which feed on roots. (From North Dakota Agriculture, 2017-18 edition, North Dakota Dept. of Agriculture.)
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References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"